Robert Mitchum's character was wounded and needed to use a crutch, but Mitchum would switch which arm he used with the crutch throughout shooting. The continuity was so poor that John Wayne (who actually worked continuity in silents while a star college football player, a method used by Hollywood fans to slip players some spending money) had his character mention it in one of the last scenes. Director Howard Hawks enjoyed it so much he left it in the movie. Mitchum's version of this story is that he objected but Hawks had him switch sides with the crutch based on what looked best in that scene. When Hawks saw how bad it looked in the dailies, Mitchum suggested the additional dialogue between his character and Wayne's to cover the gaffe.
Arch-conservative John Wayne did not get along with actor Edward Asner, whose politics were quite liberal, during filming, and constantly referred to Asner as "that New York actor". Asner later said he did not know if the phrase was intended to be an anti-Semitic insult.
The poem "El Dorado" has four verses. James Caan's character recites three, omitting the second, which laments the aging knight's failure to locate El Dorado. He recites the first verse and part of the fourth riding with John Wayne after they meet for the first time, the third when Wayne is about to ride out for the final gunfight, and the complete fourth when he himself takes up the second wagon's reins.
Robert Mitchum initially played the alcoholic sheriff as a weak and pathetic character, but Howard Hawks decided this was too similar to Dean Martin's portrayal of the drunken deputy in Rio Bravo (1959). Thereafter it was decided that Mitchum would play J.P. Harrah mostly for laughs.
Robert Mitchum revealed in an interview that when Howard Hawks asked him to be in the film, Mitchum asked what was the story of the film. Hawks reportedly replied that the story didn't matter because the film had some "great characters".
John Wayne was disappointed that the movie was released at the same time as his next movie, The War Wagon (1967). However, despite this film receiving generally poor reviews and being seen as old-fashioned and out of tune with the times, both movies proved to be hugely successful at the box office.
John Wayne cocks a Winchester lever-action rifle with one hand by twirling it by its lever. The rifle used in that shot has an enlarged "D-loop" lever to make the trick easier. John Wayne used this type of modified Winchester and performed this trick in a number of his Westerns, beginning with Stagecoach (1939).
In one scene Bull plays his harmonica. If you listen carefully you'll hear that the tune sounds like "Love MeTender." It is most likely the Civil War song "Aura Lee" on which "Love Me Tender" was based. This would make more sense in the historical era of the story.
The opening credits feature a montage of original paintings that depict various scenes of cowboy life in the Old West. The artist was Olaf Wieghorst, who appears in the film as the Gunsmith, Swede Larsen.
Leigh Brackett wrote the original script which she described as "the best script I had ever done in my life. It wasn't tragic, but it was one of those things where Wayne died at the end." However she says the closer they got to production "the more we got into doing Rio Bravo (1959) over again the sicker I got, because I hate doing things over again. And I kept saying to Howard I did that, and he'd say it was okay, we could do it over again."
The scene in which Thornton pushes one of McLeod's mooks through a door to be shot by his own men echoes a similar one from The Big Sleep (1946), which was also directed by Howard Hawks and written by Leigh Brackett.
The cast includes two lead actors from the TV Western "The Rifleman" (1958): Johnny Crawford (Luke MacDonald) played the title character's son Mark McCain, while Paul Fix (Dr. Miller) played Marshal Micah Torrance. Additionally, in the series star Chuck Connors used a Winchester with a distinctive enlarged lever, similar to the kind John Wayne uses in the film and many other of his Westerns.
Before and after the shootout in the church the gun used by the robert mitchum character is clearly seen to be a single action colt style revolver. But during the actual shootout, in order to shoot very rapidly, the robert mitchum character (drunken sheriff) can be seen squeezing the trigger without cocking for each shot on a modern double action revolver, in a closeup shot from the front. Probably it was a smith and wesson or colt variant m1917 45 because the bore size was appropriate.
The trivia item below may give away important plot points.
The ingredients that Mississippi recites for Johnny Diamond's recipe to sober up J. P. Hara are: cayenne pepper, hot mustard powder, ipecac, asafoetida, and croton oil. Ipecac is a strong emetic, asafoetida is a spice known for its strong sulfurous odor, and croton oil is a potent purgative. Anyone who administered this combination in real life would likely be shot a day or two later when the patient could finally leave the outhouse, assuming the unfortunate victim had not died of dehydration from the violent fluid diarrhea croton oil causes. The recipe also called for gunpowder, which causes nausea